It has previously been proposed to utilize sensing apparatus, such as microphones, which sense the Korotkoff noise, and to so evaluate the obtained outputs from the microphone that blood pressure values can be derived therefrom. Blood pressure apparatus of this type, which operate according to the Riva-Rocci method, have previously been described--see German Pat. No. 29 45 126. This patent discloses that the overall frequency band of the Korotkoff noises are sensed, a small frequency band is filtered therefrom, and the associated amplitudes are then determined. By use of a switching logic, the Korotkoff noises which first arise, and the Korotkoff noises which last arise, as the pressure in a blood pressure measurement cuff is decreased, are evaluated. Thus, the systolic and the diastolic blood pressures can be determined.
It is possible to eliminate interference and disturbance noises by special circuitry. It has been found, however, that the apparatus is subject to malfunction and disturbance with respect to decrease in amplitude. This may result, for example, from unsuitable positioning of the microphone used to sense the Korotkoff noises, or other inappropriate measurement procedures.